I understand that polo way is basically the same (just in different order), but much easier for use and have less friction.
Yes, this is what I am talking about. Just forget about their higher leverage for a moment (although this is also important factor). The hole process of shorting at polo is one simple action: you place a sell order. To settle your debt, you place a buy order. The final result is the same as in BTS, but everything is seamless, and you don't need to make unnecessarily high deposits. The mechanics behind this is very simple, and I don't see a reason why it should not work at DEX. You can still use your bitAssets as money, i.e. buy/sell/transfer etc.
The amount of collateral which you need to put upfront depends on the price at which you short sell your asset. If you short at feed price, you need to put only MCR-1 upfront, because the rest you get when you sell your asset, and before that you don't have no dept. If you sell at premium, you need to put less upfront, if you sell at discount, you need to put more. If you want to short, but don't want to sell, you need to put entire collateral upfront and then do what you want with your asset, same as you do now.
Same goes with closing position. It is ridiculous that you need to deposit additional funds on top of collateral to settle your debt on DEX, or find other workarounds, because the only purpose of collateral is to be used to settle the debt. And again, the amount of collateral which you need to spend depends on the price at which you buy back you debt, cheaper you buy, less you spend. If somebody kindly sends you bitAsset for free, you just keep your collateral.